Taxonomy is the science of classifying organisms. The system currently used by taxonomists is called the Linnaean taxonomic system, in honor of Swedish biologist Carolus Linnaeus (1707 — 1778). The Linnaean system breaks down organisms into seven major divisions, called taxa (singular: taxon). The divisions are as follows:
- Major Taxonomic Levels
Note: There are many subdivisions of the seven main taxonomic levels, such as Subphylum, Subclass, Infraclass, and so on. You may see many of these other sublevel taxa listed in the taxonomic tree of an organism.
The classification levels become more specific towards the bottom. Many organisms belong to the same kingdom, fewer belong to the same phylum, and so on, with species being the most specific classification. A species is one group of genetically distinct, interbreeding organisms. The average genetic differences within a species are less than the average differences between that species and a closely related group of organisms.
The classifications also tell something about the degree of relation between different organisms. For example, two animals that belong to the same family and genus are more closely related than two animals that simply belong to the same family.
Here are two examples of the Linnaean taxonomic system of classification, for humans and armadillos:
|Common Name:||Human||Nine-Banded Armadillo|
|Species:||Homo sapiens||Dasypus novemcinctus|
Note: Cingulata used to be called Xenarthra, named for a small bony bump found on the vertebrae of some members of this order. Before that, Cingulata was known as Edentata, meaning “without teeth”. Both of these earlier names have fallen out of favor: Xenarthra is now elevated to the level of a superorder, while Edentata is not accurate, as most cingulates do in fact bear teeth. Many sources will still incorrectly list Xenarthra or Edentata as the order.
The taxonomic tree above tells us that humans and armadillos are related, but not closely. We share the same class, but belong to different orders.
Most of the information at the higher levels is not included in the standard description of an organism. For most plants and animals, just listing the family, genus or species is enough to let biologists know what the other levels should be. The most common way to list the taxonomic name of an organism is to list the genus and species; this is known as binomial nomenclature, meaning a two-name system. When using this listing, the genus should always be italicized and capitalized, while the species is not capitalized. You may have noticed that in the example above I included the genus name in with the species. This is the preferred way of listing species, to avoid confusion. There could possibly be another organism with the species name sapiens, for example, but there is only one Homo sapiens.
The taxonomic names are usually in Latin, although species are often named after the person who first described them. Using Latin helps to give a general description of the organism through its taxonomic classification. For example (using the nine-banded armadillo again):
|Common Name:||Nine-Banded Armadillo||Translation:|
|Kingdom:||Animalia||Animals: Multicellular, heterotrophic, eukaryotic organisms.|
|Phylum:||Chordata||Chordates: animals with a notochord.|
|Subphylum:||Vertebrata||Vertebrates: Animals with bony spines.|
|Class:||Mammalia||Mammals: animals that have hair and give milk to their young.|
|Subclass:||Eutheria||Placentals: Mammals in which the young develop in a placenta inside the uterus.|
|Superorder:||Xenarthra||Xenarthrans: Anteaters, armadillos, and sloths. Named for their xenarthrous processes, a small bony bump on the vertebrae that is unique to this group.|
|Order:||Cingulata||Cingulata: Pampatheres (extinct), glyptodonts (extinct) and armadillos.|
|Family:||Dasypodidae||From Dasypodis, Greek for “turtle-rabbit”; Linnaeus did not like the Aztec name, Azotochtli, and so used a Greek equivalent to name the family.|
|Genus:||Dasypus||Dasypus is derived from the same Greek root as the family name.|
|Species:||Dasypus novemcinctus||Novem: nine; -cinctus: band. Nine-banded.|
The descriptive names work for other species as well. So long as you understand some Latin, you can learn a lot about an organism from its scientific name. For example, look at our own species name: Homo sapiens. Homo means “self” or “same”, meaning “the same as me” — which, for you, means “human”. Sapiens means “wise”. Therefore, Homo sapiens means “Wise human”.
Now that you know a little more about the taxonomic system, you can impress your friends! When they say, “Hey, look at that critter! What is it?” you can reply, in a calm and official-sounding voice, “That’s a D. novemcinctus, no doubt about it.”